Background: Expanding Internet-based interventions for substance use will have little benefit if heavy substance users are unlikely to have Internet access. This paper explored whether access to the Internet was a potential barrier to the provision of services for smokers, drinkers and illicit drug users. Methods: As part of a general population telephone survey of adults in Ontario, Canada, respondents were asked about their use of different drugs and also about their use of the Internet. Results: Pack-a-day smokers were less likely (48%) to have home Internet access than non-smokers (69%), and current drinkers (73%) were more likely to have home access than abstainers (50%). These relationships remained true even after controlling for demographic characteristics. Internet access was less clearly associated with cannabis or cocaine use. Conclusions: Even though there is variation in access among smokers, drinkers and illicit drug users, the World Wide Web remains an excellent opportunity to potentially provide services for substance abusers who might never access treatment in person because, in absolute terms, the majority of substance abusers do use the Internet.